doi:10.1098/rspb.2007.0461
Genetic and environmental contributions to population group differences on the Raven’s Progressive Matrices estimated from twins reared together and apart J. Philippe Rushton 1, *, Trudy Ann Bons 1 , Philip A. Vernon 1 and Jelena C ˇ vorovic´ 2 1 Department of Psychology, University of Western Ontario, London, Ontario, Canada N6A 5C2, Canada 2 Serbian Academy of Sciences, 11000 Belgrade, Serbia We carried out two studies to test the hypothesis that genetic and environmental influences explain population group differences in general mental ability just as they do individual differences within a group. We estimated the heritability and environmentality of scores on the diagrammatic puzzles of the Raven’s Coloured and/or Standard Progressive Matrices (CPM/SPM) from two independent twin samples and correlated these estimates with group differences on the same items. In Study 1, 199 pairs of 5- to 7-year-old monozygotic (MZ) and dizygotic (DZ) twins reared together provided estimates of heritability and environmentality for 36 puzzles from the CPM. These estimates correlated with the differences between the twins and 94 Serbian Roma (bothrsZ0.32;NsZ36;ps!0.05). In Study 2, 152 pairs of adult MZ and DZ twins reared apart provided estimates of heritability and environmentality for 58 puzzles from the SPM. These estimates correlated with the differences among 11 diverse samples including (i) the reared-apart twins, (ii) another sample of Serbian Roma, and (iii) East Asian, White, South Asian, Coloured and Black high school and university students in South Africa. In 55 comparisons, group differences were more pronounced on the more heritable and on the more environmental items (meanrsZ0.40 and 0.47, respectively;NsZ58;ps!0.05). After controlling for measurement reliability and variance in item pass rates, the heritabilities still correlated with the group differences, although the environmentalities did not. Puzzles found relatively difficult (or easy) by the twins were those…